A wing of an airplane usually comprises a lower wing cover, an upper wing cover, and at least one wing spar spanning the lower wing cover with the upper wing cover. Such a wing spar is frequently composed of a top chord and a bottom chord as well as a middle web therebetween. Such a spar is connected at the top chord side to the upper wind cover and at the bottom chord side to the lower wing cover.
When constructing the interface area between wing spar and wing covers, a plurality of design criteria have to be considered, such as static strength, deformation behavior, stability, crack initiation and crack growth properties, residual strength, corrosion resistance, controllability, and various production aspects.
Conventionally, a wing spar is connected to the wing covers by means of single to three row rivet joints or by means of threaded joints. It is also known from the state of the art to secure a wing spar to wing covers by using an adhesive joint. The wing covers start before a front spar connection for receiving a wing tip and end after a rear spar connection by forming the wing box for securing wing flaps.
Wing covers and wing spars have numerous thickness gradations in view of reaching minimum weight while meeting sophisticated strength requirements and maintainability requirements, like controllability or repairability. In particular for large transport airplanes, the spars are frequently integrally milled from an aluminum blank, whereas for smaller airplanes, the spars are frequently produced in differential style.
Hereafter, with reference to FIG. 1, an airplane wing 100 according to the state of the art is described.
The airplane wing 100 comprises an upper wing cover 101 and a lower wing cover 102, wherein the upper wing cover 101 is spanned with respect to the lower wing cover 102 by means of a wing spar 103. The wing spar 103 comprises a top chord 104, a bottom chord 105 and a middle web 106 arranged therebetween. The top chord 104 is connected to the upper wing cover 101 by means of a threaded joint 107. The bottom chord 105 is connected to the lower wing cover 102 by means of another threaded joint 108. The wing spar 103 is a wing spar with rib connection. As an alternative to the threaded joint 107, 108, a riveted joint can also be provided.
The connecting technique known from the state of the art for connecting the wing spar to the wing covers has considerable disadvantages. A short incipient crack durability results from high load transmission from the spar chords into the wing covers in case of wing bending or wing torsion. The single to three row rivet joints or threaded joints, which extend in wing span direction, generate high production costs, which are further increased through required durability increasing measures (e.g. plastic expansion of bores before insertion of the connecting elements).
Frequently, the chords of the spars are the components having the lowest durability, with possible cracks in general growing perpendicularly to the spar direction. Locating this crack configuration through external visual controls is frequently impossible, so that internal cost-intensive wing controls are necessary for damages to be detected in good time. Once the spar chord is broken, in many cases the required design loads (limit loads) can no longer be transmitted.
The riveted or threaded joint between wing spar and wing covers requires doubling and weight disadvantages resulting therefrom.